Ceramics have been used as coatings or as fabricated parts and are employed wherever their characteristics such as durability, nonporosity, electrical conductivity or nonconductivity, and heat protection are required. One of the more recent ceramic materials is a silicon-carbon-oxygen system, named as a black glass, which can find use in certain situations where extremely high temperatures are present. The parent applications provide an extended discussion of the art which is incorporated by reference herein. The following discusses a few of the more significant related portions of the earlier art.
Traditionally, the introduction of carbon in glasses was made by impregnating porous glass with a concentrated solution of an organic compound and subsequently firing in a reducing or neutral atmosphere. The carbon-containing product is generally regarded as a composite containing carbon and silica. See for example, Elmer and Meissner (Journal of the American Ceramic Society, 59, 206, 1976) and Smith & Crandall, U.S. Pat. No. 3,378,431.
Carbon-modified silica glass has been used as a composite matrix by Larsen, Harada and Nakamum (Report No. AFWAS-TR-83-4134, December, 1983, Wright-Patterson AFB, Ohio). In producing fiber-reinforced composites, the processing sequence includes slurry impregnation of silicon carbide fiber in an aqueous slurry of a carbowax (polyethylene glycol) and a silicon-containing compound known in the trade as Cab-O-Sil (a silicon dioxide powder manufactured by Cabot), layout of prepregged fiber tows, and hot-pressing.
More recently, formation of carbonaceous ceramics has been carried out through the use of the sol-gel process. For example, January discloses in U.S. Pat. No. RE 32,107 the use of the sol gel process to form monolithic glasses containing carbon through pyrolysis of the gels of organosilsesquioxanes, metal oxides and metal alkoxides. The gelling process is based on the following reaction: EQU .ident.Si--OR+H.sub.2 O.fwdarw..ident.Si--OH+ROH (1) EQU .ident.Si--OH+HO--Si.ident..fwdarw..ident.Si--O--Si.ident.+H.sub.2 O(2)
in which R represents an organic radical such as alkyl groups and aryl groups such as phenyl group.
Although the sol-gel process can produce homogeneous, purer glassy products by low temperature processes, monolithic black glasses produced via hydrolysis and condensation of organoalkoxysilanes require very long drying periods and delicate gelling conditions. The very slow drying rate is necessary for reducing cracks during the gelation period. These cracks form as a result of the non-uniform surface tensions created by the evaporation of the water or alcohol molecules produced in the hydrolysis (1) and condensation (2) reactions.
N. Harada and M. Tanaka in U.S. Pat. No. 3,957,717 described and claimed an organopolysiloxane gel prepared from cyclosiloxanes and H. Lamoreaux in U.S. Pat. Nos. 3,197,432 and 3,197,433 claimed the product gel from reacting cyclosiloxanes containing hydrogens and vinyl groups. The basic idea of reacting silyl hydrogen groups with silyl vinyl groups is found in U.S. Pat. Nos. 3,439,014 and 3,271,362.
Liebfried, in U.S. Pat. No. 4,900,779, discloses polymers which combine cyclic polysiloxanes or tetrahedral siloxysilanes with polycyclicpolyenes having no silicon atoms. In U.S. Pat. No. 5,013,809, Liebfried suggests including linear short chain .ident.SiH terminated polysiloxanes to the compositions of the '779 patent. Pyrolysis of these polymers to form ceramics is suggested. In U.S. Pat. No. 4,877,820, Cowan discloses a related composition in which polycyclicpolyenes are combined with poly(organohydrosiloxanes).
The present invention is concerned with the product of pyrolyzing polymers formed from silicon compounds to produce black glasses which are similar to those disclosed in the parent disclosures, USSN 07/002,049 and 07/816,269, but are derived from mixtures of cyclosiloxanes with non-cyclic siloxanes.